WO2009003744A1

WO2009003744A1 - Method for producing (meth)acrylates

Info

Publication number: WO2009003744A1
Application number: PCT/EP2008/055667
Authority: WO
Inventors: Guido Protzmann; Harald Trauthwein; Joachim Knebel; Thorben SCHÜTZ; Gerhard Kölbl; Thomas Kehr; Günter LAUSTER
Original assignee: Evonik Röhm Gmbh
Priority date: 2007-07-05
Filing date: 2008-05-08
Publication date: 2009-01-08
Also published as: EP2162423A1; CN101337889A; DE102007031470A1; JP2010532328A; TW200909409A; US20100204509A1; RU2010103714A; BRPI0814012A2; CA2692615A1; US8049030B2; KR20100036303A; AU2008271501A1

Abstract

The invention relates to a method for producing (meth)acrylates, comprising the transesterification of an alcohol with a low-boiling ester of the (meth)acrylic acid in the presence of catalysts, the alcohol released by the low-boiling ester of the (meth)acrylic acid being removed by distillation. The invention is characterized in that the mole ratio of the low-boiling ester of the (meth)acrylic acid to the feedstock alcohol present in the reaction mixture is increased during the reaction by adding low-boiling esters of the (meth)acrylic acid. The method according to the invention allows an especially cost-effective production of high-purity (meth)acrylates.

Description

Process for the preparation of (meth) acrylates

The present invention relates to processes for the preparation of (meth) acrylates.

(Meth) acrylates are well-known and widely used monomers.

Accordingly, various methods are known to obtain these compounds. For the preparation of special (meth) acrylates are many

Transesterification reactions carried out in which methyl methacrylate is reacted with a corresponding alcohol. To improve the yield and the

Selectivity of the reaction were previously used different catalysts.

For example, the document DE 28 05 702 describes the preparation of esters of unsaturated carboxylic acids. In particular, compounds containing zirconium and / or calcium can be used to catalyze the reactions described. Particularly suitable catalysts include in particular zirconium acetylacetonate. The reactions lead to high yields of about 97%, based on the alcohol used.

Furthermore, acids or bases can be used to catalyze the transesterification. Such reactions are set forth, for example, in CN 1355161, DE 34 23 443 or EP-A-0 534 666. The basic catalysts include in particular lithium amide, as exemplified in the publications DE 34 23 443, CA 795814 and US 6,194,530. In addition, it has been proposed to improve the economy of production by adding the starting compounds in the course of the reaction. Thus, for example, the document US Pat. No. 5,072,027 describes an addition of alcohol and methyl methacrylate after a high conversion of the starting compounds used at the beginning of the reaction. An increase in the molar ratio during the reaction is not described in this document.

The above-described reactions already lead to high sales and to pure products. Due to the high economic importance of specialty (meth) acrylates, however, there is a continuing effort to further improve the production of these compounds.

task

In view of the prior art, it was an object of the present invention to provide a process for the preparation of (meth) acrylates in which the product can be obtained very economically. In addition, the obtained (meth) acrylate should contain only very small amounts of by-products and catalyst residues.

Another object of the invention was to provide a method in which (meth) acrylates can be obtained very selectively.

In addition, it was an object of the present invention to provide processes for the preparation of (meth) acrylates, which can be carried out simply and inexpensively. The product should be obtained in high yields and, if possible, with low energy consumption. solution

These and other non-explicitly stated objects, which, however, are readily derivable or deducible from the contexts discussed hereinbelow, are solved by methods having all features of claim 1. Advantageous modifications of the inventive methods are protected by the dependent claims appended to claim 1 posed.

The present invention accordingly provides a process for the preparation of (meth) acrylates which comprises the transesterification of an alcohol with a low-boiling ester of (meth) acrylic acid in the presence of catalysts, wherein the alcohol released from the low-boiling ester of (meth) acrylic acid is separated by distillation, which is characterized in that the present in the reaction mixture molar ratio of low-boiling ester of (meth) acrylic acid to educt alcohol during the reaction by adding low-boiling ester of (meth) acrylic acid is increased.

This makes it possible to provide a method for the production of (meth) acrylates in an unpredictable manner, in which the product is obtained very economically. Surprisingly, the product obtained contains only very small amounts of by-products and catalyst residues.

Furthermore, the process according to the invention enables a particularly selective preparation of (meth) acrylates. Furthermore, the inventive method can be carried out easily and inexpensively, the product can be obtained in high yields and, overall, with low energy consumption.

In addition, a particularly high utilization of the vessel volume can be achieved by the method according to the invention, so that large amounts of special (meth) acrylates can be produced even with relatively small plants. Furthermore, the amount of specialty (meth) acrylate produced per batch can be increased so that further benefits can be achieved as the cost of carrying out the reaction relative to the amount of product obtained decreases.

According to the invention, (meth) acrylates are prepared, the term (meth) acrylate being methacylate, acrylate and mixtures of methacrylates and acrylates. (Meth) acrylates are well known in the art. These compounds include, but are not limited to, (meth) acrylates derived from saturated alcohols such as hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, heptyl (meth) acrylate, 2- (tert-butylamino) ethyl (meth ) acrylate, octyl (meth) acrylate, 3-iso-propylheptyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, undecyl (meth) acrylate, 5-methylundecyl (meth) acrylate, dodecyl (meth) acrylate , 2-methyldodecyl (meth) acrylate, tridecyl (meth) acrylate,

5-methyltridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, 2-methylhexadecyl (meth) acrylate, heptadecyl (meth) acrylate, 5-iso-propylheptadecyl (meth) acrylate, 4-tert-butyloctadecyl (meth) acrylate, 5-ethyloctadecyl (meth) acrylate, 3-iso-propyloctadecyl (meth) acrylate, octadecyl (meth) acrylate,

Nonadecyl (meth) acrylate, eicosyl (meth) acrylate, cetyleicosyl (meth) acrylate,

Stearyl eicosyl (meth) acrylate, docosyl (meth) acrylate and / or eicosyl tetratriacontyl

(Meth) acrylate;

(Meth) acrylates derived from unsaturated alcohols, such as. 2-propynyl (meth) acrylate, allyl (meth) acrylate, vinyl (meth) acrylate, oleyl (meth) acrylate; Cycloalkyl (meth) acrylates, such as cyclopentyl (meth) acrylate,

3-vinylcyclohexyl (meth) acrylate, cyclohexyl (meth) acrylate, bornyl (meth) acrylate;

(Meth) acrylates having two or more (meth) acrylic groups,

Glycol di (meth) acrylates, such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetra- and

Polyethylene glycol di (meth) acrylate, 1,3-butanediol (meth) acrylate,

1, 4-butanediol (meth) acrylate, 1,6-hexanediol di (meth) acrylate, glycerol di (meth) acrylate and dimethacrylates of ethoxylated bisphenol A; (Meth) acrylates having three or more double bonds, e.g. Glycehneth (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate and

Dipentaerythhtpenta (meth) acrylate.

Particularly preferred (meth) acrylates include, in particular, ethylene glycol dimethacrylate (2-methyl-1-propenoic acid diester, CAS number 97-90-5), 1,3-butanediol dimethacrylate (CAS No. 1189-08-8), 1, 4-butanediol dimethacrylate (CAS number 2082-81 -7) and / or trimethylolpropane trimethacrylate.

For the preparation of the (meth) acrylates, an alcohol is used according to the invention, which is also referred to herein as Eduktalkohol. The type of alcohol results here from the intended target compound. Accordingly, in particular, alcohols having 5 or more carbon atoms, unsaturated alcohols and / or polyhydric alcohols can be used. The preferred alcohols having 5 or more carbon atoms include, for example, pentanol, hexanol, 2-ethylhexanol, heptanol, 2-tert-butylheptanol, octanol, 3-iso-propylheptanol, nonanol, decanol, undecanol, 5-methyl undeanol, dodecanol, 2- Methyldodecanol, tridecanol, 5-methyltridecanol, tetradecanol, pentadecanol, hexadecanol, 2-methylhexadecanol, heptadecanol, 5-iso-propylheptadecanol, 4-tert-butyloctadecanol, 5-ethyloctadecanol, 3-iso-propyloctadecanol, octadecanol, nonadecanol, eicosanol, cetyleicosanol , Stearyleicosanol, Docosanol and / or eicosyltetratriacontanol. The preferred unsaturated alcohols include in particular 2-propyn-1-ol, allyl alcohol and vinyl alcohol and / or oleyl alcohol.

Particular preference is given to the use of polyhydric alcohols. Polyhydric alcohols are organic compounds having two, three, four or more hydroxy groups. These compounds include in particular ethylene glycol, trimethylolpropane, 1, 2-propanediol, 1, 3-propanediol, 1, 3-butanediol, 1, 4-butanediol 1, 6-hexanediol, pentaerythritol, polyethylene glycol, in particular polyethylene glycol 400, and / or glycehn Trimethylolpropane is particularly preferred. The compounds are widely available commercially, for example, from BASF AG or Celanese AG.

According to the present invention, an alcohol is reacted with a low-boiling ester of (meth) acrylic acid. The term "low boiling ester" means that the ester used as a starting compound having a lower boiling point than the ester. Obtained by the transesterification at a pressure of 10 mbar, the difference of the boiling point is preferably at least 2 ° C, more preferably at least 10 ⁰ C and very particularly preferably at least 20 ^° C. Particularly suitable (meth) acrylates are formed, in particular, of alcohols having 1 to 4 carbon atoms and include, in particular, methanol, ethanol, n-propanol, isopropanol, n-butanol and tert-butanol Particular preference is given in particular to ethyl (meth) acrylate or methyl (meth) acrylate, with methyl methacrylate being very particularly preferred.

The weight ratio of starting alcohol to low-boiling ester of methacrylic acid is preferably in the range from 1: 2 to 1:20, more preferably from 1: 5 to 1:15, and most preferably in the range from 1: 6 to 1:10. The transesterification according to the invention preferably takes place in the presence of catalysts. The catalysts which can be used for this purpose are known per se, these being listed in detail in the prior art set out above. These include in particular compounds of zirconium, such as zirconium acetylacetonate. The CAS number of zirconium acetylacetonate is 17501-44-9. The preparation of zirconium acetylacetonate from acetylacetone (pentane-2,4-dione) and zirconium compounds is described for example in Houben-Weyl, Methods of Organic Chemistry, 4th edition, Bd. VI / 2, 1963, pages 53-55 and 58 to 61 and in AE Martell, M. Calvin, "The Chemistry of Metal Chelate Compounds" (1958). Advantageously, from 0.2 to 5 mmol, more preferably 0.5 to 2 mmol zirconium acetylacetonate can be used per mole of transesterifying alcohol. The preparation of the catalyst can also be carried out in situ, wherein the starting materials can be added before or during the transesterification of the reaction mixture.

Especially useful catalysts may be used which comprise lithium compounds and / or calcium compounds, wherein at least one of the compounds of lithium and / or calcium is an oxide, a hydroxide, an alkoxide having 1 to 4 carbon atoms or a carboxylate having 1 to 4 carbon atoms , Preferably, the catalyst comprises at least one lithium compound selected from the group consisting of lithium chloride (LiCl), lithium amide (LiNH ₂ ) lithium oxide (Li ₂ O), lithium hydroxide (LiOH), lithium alcoholate having 1 to 4 carbon atoms, such as lithium methoxide (Li (CH ₃ O) )

Lithiumethanolat (Li (CH ₃ CH ₂ O)) and / or lithium carboxylate having 1 to 4 carbon atoms, such as lithium acetate, and at least one calcium compound selected from the group of calcium oxide (CaO), calcium hydroxide (Ca (OH) ₂ ), calcium with 1 to 4 carbon atoms, such as calcium methoxide (Ca (CH ₃ O) ₂ ), calcium ethanolate (Ca (CH ₃ CH ₂ O) ₂ ) and / or Calcium carboxylate having 1 to 4 carbon atoms, such as calcium acetate.

The compounds of lithium and / or calcium may preferably be basic in nature, i. when dissolved in water there is an increase in the pH.

Suitably, the catalyst may contain as lithium compound, for example, lithium hydroxide (LiOH), lithium oxide (Li ₂ O), lithium methoxide (Ca (CH ₃ O) ₂ ) and / or lithium ethoxide (Li (CH ₃ CH ₂ O)).

Also of particular interest are catalysts which contain calcium oxide (CaO), calcium hydroxide (Ca (OH) ₂ ), calcium methoxide (Ca (CH ₃ O) ₂ ) and / or calcium ethanolate (Ca (CH ₃ CH ₂ O) as calcium compound. ₂ ).

The catalyst used may preferably be a mixture which comprises lithium hydroxide and calcium oxide or lithium hydroxide and calcium hydroxide. These mixtures are especially useful for the transesterification of butanediols.

According to a further embodiment, a mixture comprising lithium amide (LiNH ₂ ) and lithium chloride (LiCl) can be used for catalysis. This mixture is suitable, for example, for the preparation of ethylene glycol dimethacrylate.

In addition, combinations of catalysis involving lithium chloride (LiCl) and calcium oxide (CaO) are particularly useful. These catalysts can be used in particular for the preparation of trimethylolpropane methacrylate. The amount of catalyst used can be in a wide range. Of particular interest, however, are processes in which the proportion of catalyst, based on the weight of the alcohol used, in the range of 0.05 to 8 wt .-%, preferably in the range of 0.01 to 5 wt .-% and especially is preferably in the range of 0.1 to 1 wt .-%.

The total amount of catalyst used can be added to the reaction mixture at the beginning of the reaction. According to a particularly expedient modification, a part of the catalyst, for example a part of the lithium mamide, can be added to the reaction mixture in the course of the reaction. Preferably, after a conversion in the range of 20 to 80%, particularly preferably in the range of 30% to 60%, based on the weight of the alcohol used, further catalyst can be added to the reaction mixture.

The reaction can be carried out at overpressure or underpressure. According to a particularly expedient modification of the present invention, the transesterification can be carried out at a pressure in the range from 200 mbar to 2,000 mbar, particularly preferably in the range from 500 mbar to 1,300 mbar.

The reaction temperature can also be in a wide range, in particular as a function of the pressure. According to a preferred embodiment of the present invention, the reaction is preferably carried out at a temperature in the range of 60 ⁰ C to 150 ⁰ C, more preferably in the range of 70 ° C to 140 ⁰ C and most preferably 90 ° C to 130 ° C.

Surprisingly, particular advantages can be achieved if the temperature at which the reaction takes place is increased in the course of the reaction. According to this preferred modification of the process according to the invention, the temperature at the beginning of the reaction, in particular up to a conversion of 80%, preferably up to a conversion of 70%, based on the weight of used alcohol, preferably in the range of 90 ⁰ C to 110 ⁰ C and towards the end of the reaction, in particular after a conversion of 80%, preferably after a conversion of 90%, based on the weight of the alcohol used, in the range of 115 ° C. to 130 ⁰ C. lie.

The process according to the invention can be carried out in bulk, i. be carried out without the use of another solvent. If desired, an inert solvent can also be used. These include, but are not limited to, benzene, toluene, n-hexane, cyclohexane and methyl isobutyl ketone (MIBK) and methyl ethyl ketone (MEK).

In a particularly useful variant of the transesterification according to the invention, all components, such as, for example, the alcohol, the methacrylic acid ester and the catalyst, are mixed, after which this reaction mixture is heated to boiling. Subsequently, the liberated alcohol, for example methanol or ethanol, can be removed by distillation, optionally azeotropically with methyl methacrylate or ethyl methacrylate, from the reaction mixture.

The reaction times depend, among other things, on the selected parameters, such as pressure and temperature. However, they are generally in the range of 1 to 24 hours, preferably 5 to 20 hours and most preferably 6 to 12 hours. In continuous processes, the residence times are generally in the range of 0.5 to 24 hours, preferably from 1 to 12 hours and most preferably 2 to 3 hours. Further references with regard to the reaction times can be found by the person skilled in the art in the attached examples. Preferably, the reaction may take place with stirring, wherein the stirring speed may be more preferably in the range of 50 to 2000 rpm, most preferably in the range of 100 to 500 rpm.

The pH can be in a wide range. Appropriately, the

Reaction at a pH in the range of 8 to 14, preferably 9 to 13 are performed.

In order to prevent unwanted polymerization of the methacrylates, polymerization inhibitors can be used in the reaction. These compounds, such as hydroquinones, hydroquinone ethers, such as hydroquinone monomethyl ether or di-tert-butyl catechol, phenothiazine, N, N '- (diphenyl) - p-phenylenediamine, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1 oxy, p-phenylenediamine, methylene blue or hindered phenols are well known in the art. These compounds can be used singly or in the form of mixtures and are generally available commercially. The effect of the stabilizers is usually that they act as radical scavengers for the free radicals occurring during the polymerization. For further details, reference is made to the usual technical literature, in particular to the Rompp-Lexikon Chemie; Publisher: J. Falbe, M. Regitz; Stuttgart, New York; 10th edition

(1996); Reference "Antioxidants" and cited references cited here.

In particular, phenols are preferably used as the polymerization inhibitor. Particularly surprising advantages can be achieved when using hydroquinone monomethyl ether. Based on the weight of the total reaction mixture, the proportion of inhibitors individually or as a mixture can generally be 0.01-0.5% (wt / wt). These polymerization inhibitors may be added to the reaction mixture before or at the beginning of the reaction. In addition, parts of the accompanying polymerization inhibitors may also be added during transesterification. Of particular interest here are in particular processes in which part of the polymerization inhibitor is added via the column reflux. Particularly useful are, inter alia, mixtures containing methyl methacrylate, hydroquinone monomethyl ether and 4-hydroxy-2, 2,6,6-tetramethylpiperidine-1-oxyl. By this measure, in particular an undesired polymerization within the distillation column can be avoided.

In addition, oxygen can be used for inhibition. This can be used, for example, in the form of air, wherein the amounts are advantageously metered so that the content in the gas phase above the reaction mixture remains below the explosion limit. Air quantities in the range of 0.05 to 0.5 l per hour and moles of alcohol are particularly preferred. In batch processes, this amount may refer to the amount of alcohol originally used. In continuous processes, this amount may refer to the amount of alcohol added. Similarly, inert gas-oxygen mixtures, e.g. Nitrogen-oxygen or argon-oxygen mixtures are used.

According to a particular embodiment of the present invention, a combination of oxygen with at least one phenol, preferably hydroquinone monomethyl ether, can be used for the inhibition.

The alcohol released from the (meth) acrylate used, for example methanol and / or ethanol, is separated by distillation. In this case, for example, a mixture containing methyl methacrylate and methanol can advantageously be separated off. Surprisingly, a part can be beneficial the separated mixture in the following approach. According to this modification, the recyclable fraction of the separated mixture can be obtained at the end of the reaction, in particular after a conversion of 80%, preferably after a conversion of 90% of the alcohol used. For example, the proportion of the recirculated mixture at the beginning of the following batch in the range of 10 to 50%, based on the total Wewaesterdem to be transesterified methacrylic ester.

The transesterification can be carried out both continuously and batchwise. The inventive increase in the molar ratio of low-boiling ester of (meth) acrylic acid to educt alcohol by the addition of low-boiling ester of (meth) acrylic acid during a continuous reaction can be carried out, for example, in particular in systems with multiple reactors.

Of particular interest are, in particular, semibatch processes in which a part of the reaction mixture is initially charged. In further steps or continuously, after the reaction has started, low-boiling esters of (meth) acrylic acid can be added to the reaction mixture.

According to a particular embodiment, the amount of low-boiling ester of (meth) acrylic acid added can be controlled by the amount of alcohol released from the reaction mixture. To control, for example, the temperature can be used, which sets in the column at a suitable height. Also, the reflux ratio can be adjusted via the temperature in the column during the removal by distillation of the liberated from the educt alcohol. For example, a mixture separated from the reaction mixture, summarizes the methanol and methyl methacrylate environmentally, so a temperature of about 75 ⁰ C to 85 ° C can be given over a longer period above which no distillate is withdrawn. First below this temperature, an appropriate amount of a mixture is separated. As a result, it can be achieved that a relatively high ratio of low-boiling (meth) acrylate to educt alcohol is maintained over a long period of time without the reaction mixture having to be supplied with excessively high amounts of low-boiling (meth) acrylate.

Essential for the success of the invention is that the present in the reaction mixture molar ratio of low-boiling ester of (meth) acrylic acid to educt alcohol during the reaction by adding low-boiling ester of (meth) acrylic acid is increased. The term "low boiling ester addition" means that this compound is fed from an external source, and pure reflux, which occurs within the distillation column, is therefore not an addition Molar ratio of the proportion of low-boiling ester of (meth) acrylic acid to the proportion of alcohol used for transesterification during the reaction by adding low-boiling esters of (meth) acrylic acid by at least 10%, more preferably at least 40% and most preferably at least By way of example, the molar ratio of the low-boiling ester added during the reaction to the amount of low-boiling ester used at the start of the reaction may be in the range from 1: 5 to 2: 1, more preferably from 1: 3 to 1: 1, 5 may suitably be the weight ratio of educt alcohol to low The boiling esters of (meth) acrylic acid at the beginning of the reaction are preferably in the range from 1: 2 to 1: 8, more preferably 1: 2.5 to 1: 6 and most preferably in the range from 1: 3 to 1: 4 , By adding low-boiling ester during the reaction, this ratio can for example be increased to 1: 3 to 1:20, preferably 1: 4 to 1:15 and most preferably 1: 6 to 1:10. These values relate in each case to the educt alcohol present in the reaction mixture. The already to Product ester reacted portion of the educt alcohol can be determined in many cases by the proportion of distilled off alcohol, which was released by the reaction. In addition, the proportion of reactant alcohol in the reaction mixture can be determined by gas chromatography.

Advantageously, the addition of the low-boiling ester of (meth) acrylic acid over a period of at least 30%, preferably at least 50% and most preferably at least 70% of the reaction time corresponds. In this case, the addition can take place in steps within this period, with the first entry specifying the beginning of this period and the last addition the endpoint of this period. Preferably, the addition is carried out in at least three, preferably at least 5, and most preferably at least 10 steps. In addition, this addition can also be done continuously.

Of particular interest are, inter alia, batch processes in which methyl methacrylate is added during the transesterification. This embodiment is advantageous, for example, if methyl methacrylate is removed from the reaction mixture together with methanol. Preferably, the weight ratio of the amount of methyl methacrylate added during the transesterification to the amount of separated methanol-methyl methacrylate mixture can be in the range from 2: 1 to 1: 2, particularly preferably 1: 5: 1 to 1: 1.5.

In the case of batch processes, excess starting material, in particular the unreacted ester of (meth) acrylic acid, can be separated by distillation towards the end of the reaction. This can also be used again in the next batch without further purification.

The distillate obtained at the beginning of the reaction, which may for example comprise large amounts of methanol or ethanol, may also be recycled be, for example, by incorporation into a plant operated in the network for the production of the transesterified (meth) acrylate ester.

A suitable plant for carrying out the present transesterification may comprise, for example, a stirred tank reactor with stirrer, steam heating, distillation column and condenser. Such systems are known per se and described for example in Ullmann's Encyclopedia of Industrial Chemistry (6th edition), Verlag Wiley-VCH, Weinheim 2003, Volume 10, page 647. The size of the plant depends on the amount of (meth) acrylate to be produced, and the present process can be carried out both on a laboratory scale and on an industrial scale. According to a particular aspect, the stirred tank reactor can accordingly have a boiler volume in the range of 1 m ³ to 30 m ³ , preferably 3 m ³ to 20 m ³ . The agitator of the reactor vessel may be designed in particular in the form of an anchor agitator, impeller, blade or inter MIG stirrer.

The task of the distillation column is to ensure that a methanol- or ethanol-rich azeotrope is removed in order to minimize the losses of inevitably discharged with Eduktester. The distillation column may have one, two or more separation stages. The number of separation stages is the number of plates in a tray column or the number of theoretical plates in the case of a packed column or a packed column. Examples of a multistage distillation column with trays include those such as bubble trays, sieve trays, tunnel trays, valve trays, slotted trays, sieve slotted trays, sieve trays, nozzle trays, centrifugal trays, for a multistage distillation column with packing such as Raschig rings, Lessing rings, Pall Rings, Berl saddles, Intalox saddles and for a multi-stage distillation column with packings such as those of the type Mellapak (Sulzer), Rombopak (Kühni), Montz-Pak (Montz). The conversion-dependent adjustment of the reflux ratio makes it possible, for example, when using methyl methacrylate lat over wide ranges of the conversion to set a methanol content in the distillate, which is above 60%.

Among the suitable capacitors that may be included in the facility for carrying out the present transesterification include plate and shell and tube heat exchangers.

After completion of the reaction, the resulting (meth) acrylate often already meets the high requirements set out above, so that further purification is often unnecessary. To further increase the quality and in particular the catalyst separation, the mixture obtained can be purified by known methods.

According to one embodiment of the method according to the invention, the product mixture obtained can be purified by filtration processes. These methods are known from the prior art (W. Gösele, Chr. Alt in Ullmann's Encyclopedia of Industhal Chemistry, (6th Edition), Verlag Wiley-VCH, Weinheim 2003, Volume 13, pages 731 and 746), whereby conventional filtration aids, for example, bleaching earth and / or aluminum silicate (perlite) can be used. For example, continuously operable filters can be used for a precoat filtration or candle filters, among others.

Further improvement of the quality of the product can be achieved, for example, by distillation of the resulting filtrate. Because of the tendency of the monomer to polymerize, distillation processes are recommended in which the thermal load of the substance to be distilled is minimized. Well suited are devices in which the monomer is continuously evaporated from a thin layer, such as falling film evaporator and evaporator with a rotating wiper system. Short-path evaporators can also be used. Such devices are known (Ullmanns Encyclopedia of Indus- mistry (6th edition), Verlag Wiley-VCH, Weinheim 2003, Volume 36, page 505). Thus, for example, a continuous evaporator with rotating wiper system and attached column can be used. The distillation can be carried out for example at a pressure in the range of 1 to 40 mbar and an evaporator temperature of 120 ⁰ C to 150 ⁰ C.

Hereinafter, the present invention will be explained with reference to examples and comparative examples, without thereby limiting it.

Comparative Example 1

In a 6m ³ stirred tank reactor with stirrer, steam heating, distillation column and condenser, 600 kg of trimethylolpropane, 3348 kg of methyl methacrylate (MMA), 0.1 kg of hydroquinone monomethyl ether as inhibitor and as catalyst a mixture of 5 kg of calcium oxide and 1 kg of lithium chloride combined and stirred with the introduction of air. For column stabilization, a total of 151 kg of MMA containing 0.12 kg of hydroquinone monomethyl ether and 0.016 kg of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl dissolved in the column reflux are metered into the column reflux during the course of the reaction. The mixture is heated to 96 ° C bottom temperature, the column is initially operated with complete reflux. As soon as the temperature at the top of the column falls below 70 ^° C., the methanol-MMA mixture is withdrawn under a reflux ratio of 8: 1. From a column head temperature of 85 ° C, the methanol-MMA mixture is low in methanol and is collected in a separate container to be reused as raw material in the next batch. When the bottom temperature reaches 115 ° C., the reaction is complete and excess MMA is removed in vacuo, gradually reducing the pressure to 100 mbar. If no MMA distils off anymore, the vacuum is released. The boiler contents, consisting of the catalyst containing Trimethylolpropantrimethacrylat is mixed with 15 kg of bleaching earth and 5 kg AIuminium silicate (perlite) as a filter aid and freed from the catalyst by precoat filtration. The filtrate is fed into a continuous evaporator (area 2 m ² ) with rotating wiper system at 15 Torr pressure and 142 ° C evaporator temperature. From the bottom product, a total of 1,420 kg of trimethylolpropane trimethacrylate is obtained.

Composition (determined by gas chromatography): 90.6% trimethylolpropane trimethacrylate 0.031% MMA

0.09% trimethylolpropane monomethacrylate

2% trimethylolpropane dimethacrylate

2.4% 2 - {[2- (methoxycarbonyl) propoxy] methyl} -2 - [(2-methylprop-2-enoyloxy) methyl] butyl 2-methylprop-2-enoate 3.5% 2 - {[2- ({2,2-bis [(2-methylprop-2-enoyloxy) methyl] butyl} oxycarbonyl) propoxy] methyl} -2 - [(2-methylprop-2-enoyloxy) methyl] butyl 2-methylprop-2 - enoat

example 1

In a 6m, 3 - stirred tank reactor with stirrer, steam heating, distillation column and condenser 775 kg of trimethylolpropane, 1 .018 kg of methyl methacrylate (MMA) and 1,433 kg MMA recyclate from Comparative Example 1, 0.123 kg of hydroquinone monomethyl ether as an inhibitor and as a catalyst mixture from 10 kg of calcium oxide and 2.5 kg of lithium chloride combined and stirred with the introduction of air. For column stabilization, a total of 151 kg of MMA containing 0.12 kg of hydroquinone monomethyl ether and 0.016 kg of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl dissolved in the column reflux are metered into the column reflux in the course of the reaction. The mixture is heated to 100 ⁰ C bottom temperature, with the column inlet next operated under complete return. As soon as the temperature at the top of the column falls below 70 ^° C., the methanol-MMA mixture is withdrawn under a reflux ratio of 4: 1. The MM A supply in the reactor is supplemented by metering in equal parts of fresh MMA per part of methanol-MMA mixture withdrawn. Within 5 h, a total of 1414 kg of MMA are introduced. Within 8 h, the reflux ratio is adjusted to 27: 1 of decreasing methanol evolution. A total of 1410 kg methanol-MMA mixture discharged. From a column overhead temperature of 85 ^° C., the methanol / MMA mixture is low in methanol and is collected in a separate container in order to be reused as raw material in the next batch. At a bottom temperature of 115 ⁰ C, the reaction is complete and it extracts excess MMA in vacuo, gradually reducing the pressure to 100 mbar. If no MMA distils off anymore, the vacuum is released. The contents of the vessel, consisting of the catalyst-containing trimethylolpropane trimethacrylate, are mixed with 18 kg of bleaching earth and 12 kg of aluminum silicate (perlite) as filter aid and freed from the catalyst by precoat filtration. The filtrate is fed to a continuous evaporator (3.5 m ^{2 area} ) with rotating wiper system at 18 torr pressure and 134 ° C evaporator temperature. From the bottom effluent, a total of 1830 kg of trimethylolpropane trimethacrylate is obtained.

Composition (determined by gas chromatography): 93.6% trimethylolpropane trimethacrylate 0.1% MMA 0.09% trimethylolpropane monomethacrylate 0.66% trimethylolpropane dimethacrylate

1.8% 2 - {[2- (methoxycarbonyl) propoxy] methyl} -2 - [(2-methylprop-2-enoyloxy) methyl] butyl 2-methylprop-2-enoate 2 - {[2 - ({2,2-bis [(2-methylprop-2-enoyloxy) methyl] butyl} oxycarbonyl) propoxy] methyl} -2 - [(2-methylprop-2-enoyloxy) -ethyl] butyl 2-methylprop-2-enoate

Claims

claims

A process for the preparation of (meth) acrylates which comprises the transesterification of an alcohol with a low-boiling ester of (meth) acrylic acid in the presence of catalysts, the alcohol released from the low-boiling ester of (meth) acrylic acid being separated off by distillation, characterized in that the present in the reaction mixture molar ratio of low-boiling ester of (meth) acrylic acid to educt alcohol during the reaction by adding low-boiling ester of (meth) acrylic acid is increased.

2. The method according to claim 1, characterized in that methyl (meth) acrylate and / or ethyl (meth) acrylate is used as a low-boiling ester of (meth) acrylic acid.

3. The method according to claim 1 or 2, characterized in that methyl methacrylate is used as a low-boiling ester of (meth) acrylic acid.

4. The method according to any one of the preceding claims, characterized in that a polyhydric alcohol is used as Eduktalkohol.

5. The method according to claim 4, characterized in that as the alcohol ethylene glycol, trimethylolpropane, 1, 2-propanediol, 1, 3-propanediol,

1, 3-butanediol, 1, 4-butanediol, 1, 6-hexanediol and / or pentaerythritol is used.

6. The method according to any one of the preceding claims, character- ized in that as catalyst at least one lithium At least one of the compounds of lithium and / or calcium is an oxide, a hydroxide, an alkoxide having 1 to 4 carbon atoms or a carboxylate having 1 to 4 carbon atoms.

7. The method according to any one of the preceding claims, characterized in that the catalyst used is a mixture comprising lithium chloride and calcium oxide.

8. The method according to at least one of the preceding claims, characterized in that the addition takes place over a period corresponding to at least 50% of the reaction time.

9. The method according to any one of the preceding claims, character- ized in that the amount of low-boiling added

Esters of (meth) acrylic acid is controlled by the amount of alcohol released from the reaction mixture.

A process according to claim 9, characterized in that the amount of alcohol released, which is separated from the reaction mixture, is controlled by the temperature in the column of the still.

11. The method according to any one of the preceding claims, characterized in that the present in the reaction mixture molar ratio of low-boiling ester of (meth) acrylic acid to Eduk- talkohol during the reaction by adding low-boiling ester of (meth) acrylic acid by at least 40th % is increased.

12. The method according to at least one of the preceding claims, characterized in that a mixture is separated, which contains methyl methacrylate and methanol.

13. The method according to any one of the preceding claims, characterized in that methyl methacrylate is added during the transesterification.

14. The method according to claim 13, characterized in that the weight ratio of the amount of added during the transesterification

Methyl methacrylate to the amount of separated methanol-methyl methacrylate mixture in the range of 2: 1 to 1: 2.

15. The method according to at least one of the preceding claims, character- ized in that the molar ratio of the low-boiling ester added during the reaction to the amount of low-boiling ester used at the beginning of the reaction in the range of 1: 5 to 2: 1.

16. The method according to any one of the preceding claims, characterized in that the reaction time is in the range of 5 to 20 hours.

17. The method according to claim 16, characterized in that the reaction onszeit in the range of 6 to 12 hours.

18. The method according to at least one of the preceding claims, characterized in that the weight ratio of starting alcohol to low-boiling ester of (meth) acrylic acid in the range of 1: 2 to 1: 20.

19. The method according to claim 18, characterized in that the weight ratio of educt alcohol to low-boiling ester of (meth) acrylic acid in the range of 1: 5 to 1: 15.

20. The method according to any one of the preceding claims, characterized in that the reaction takes place at a pressure in the range of 200 to 2000 mbar.

21. The method according to any one of the preceding claims, characterized in that the reaction takes place at a temperature in the range of 90 ⁰ C to 130 ⁰ C.

22. The method according to any one of the preceding claims, character- ized in that the temperature at which the reaction takes place, is increased in the course of the reaction.

23. The method according to claim 21 or 22, characterized in that the temperature at the beginning of the reaction in the range of 90 ° C to 110 ⁰ C and towards the end of the reaction in the range of 115 ° C to 130 ° C.

24. The method according to any one of the preceding claims, characterized in that the reaction takes place in the presence of a polymerization inhibitor.

25. The method according to any one of the preceding claims, characterized in that the reaction takes place with the introduction of oxygen.